This invention disclosed herein relates to optical fiber adapters for coupling a first plug terminated optical fiber cable to a second plug terminated optical fiber cable. In particular, it relates to such an adapter for coupling terminating plugs having dissimilar size ferrules.
In the present state of the optical fiber art, optical fibers or cables are generally terminated in plug type connectors, and coupling two fibers together is usually accomplished by use of an adapter which receives the connectors and aligns them in abutting relationship for the low-loss transmission of signals across the junction. An early type of adapter is formed as a tubular body sized and shaped to allow an alignment sleeve to pass therethrough in which the ferrules of the couplers are held in aligned, abutting relationship. An example of such an early type of coupling is disclosed in U.S. Pat. No. 5,082,345 of Cammons et al., which is adapted to couple two of the same type of optical fiber connectors together. In the Cammons patent, the ferrule of one of the connectors is introduced into one end of the alignment sleeve and the combination thus formed is passed into the adapter body. The second connector is then inserted into the adapter and its ferrule inserted into the other end of the alignment sleeve. Later developments have produced adapters wherein the alignment sleeve is contained within the adapter into which both connectors are inserted, such as is shown in U.S. Pat. No. 5,212,752 of Stephenson et al.
There have has been developed a large number of fiber (or cable) terminating connectors, some serving certain specific operational purposes, others by way of improved economy of manufacture, and others for simplicity of construction and/or use. Thus, there are differing connectors bearing the designations SC, ST(copyright), FC, LC, and MU, all of which are widely used, giving rise to the situation where, quite often, a cable having a terminating connector of one type is to be connected to a cable having a termination of a different type. An early solution to this problem is disclosed in U.S. Pat. No. 5,067,783 of Lampert et al., which discloses an optical fiber adapter or build-out system comprising first and second pieces, each for receiving a particular connector differing from the other and which, when joined together, permitted coupling of FC to ST(copyright), as well as FC to FC and ST(copyright) to ST(copyright). Although the Lampert et al. invention represents an advance in the art, the problem remains that new connector developments, such as the LC and the SC connectors, must be accommodated, and thus a more universal coupling apparatus is needed. U.S. Pat. No. 5,274,729 of King et al. discloses a universal build-out system which solves the ongoing problem of coupling the plethora of differing types of connectors together, and allows for the connection of SC, ST(copyright), and FC connectors to one another, in any combination as desired. More recently, in U.S. patent application Ser. No. 09/282,926; filed Apr. 1, 1999, and entitled xe2x80x9cUniversal Modular Fiber Build-Outxe2x80x9d, there is disclosed a system for coupling not only the large 2.5 mm diameter ferrules of SC, ST(copyright), and FC connectors to one another, but also implementing, for the first time, the coupling of the small 1.25 mm diameter ferrules of the LC connector to the large diameter ferrule of the SC, ST(copyright), and PC connectors. The alignment sleeve can take the form of a stepped sleeve of the two differing diameters. The aforementioned Sheldon et al. application Ser. No. 09/438,311 discloses similar arrangements wherein the adapter or build-out is of one piece instead of the more common two piece arrangement, thereby resulting in a less costly device.
It is standard in all of the commonly used connectors that the ferrule is movable in translation and is biased toward the coupling end of the connector generally by means of a coil spring. In a standard adapter each ferrule is biased beyond the plane of contact until the connectors are seated within the adapter, at which position the ferrules abut each other with substantially equal force and retreat from their forward position to where the plane of contact is substantially centered within the adapter, and the forces on the ferrules being equalized, the ferrules are able to move or float together in the axial direction, thereby maintaining proper alignment. However, if one of the springs has substantially greater force than the other, or if one connector has no spring, that ferrule will advance forward within the adapter until it encounters a surface that stops further movement and, as a consequence, proper alignment is degraded, the ferrules being no longer xe2x80x9cfloatingxe2x80x9d. Thus, even though the stepped sleeve accommodates the different diameter ferrules, the sleeve itself will be moved out of position due to the force of the stronger spring. When, for example, the adapter is designed to couple the large diameter (2.5 mn) ferrule of an SC type connector to the smaller diameter (1.25 mm) ferrule of the LC or MU type connector, the spring of the SC connector provides approximately two and two-tenths (2.2) pounds of force, which easily overcomes the one and two tenths (1.2) pounds of force provided by the spring of the LC or MU type connector thereby pushing the smaller ferrule out of the plane of contact, with consequent degraded alignment.
The present invention is an adapter, comprising either a one piece or a two piece body, that contains a stepped alignment sleeve for receiving, at one end, a large diameter ferrule and, at the other end, a small diameter ferrule which sleeve is contained within the adapter by means of latch gates which allow some translational movement of the sleeve. The adapter itself is sized and shaped at one end to receive a first optical fiber connector, having, for example, a large diameter ferrule, and sized and shaped at the other end to receive a second optical fiber connector having a small diameter ferrule, as taught in the aforementioned Sheldon et al. application, and the stepped alignment sleeve is adapted to receive the ferrules thereof. A transverse wall portion within the adapter from either side of which axially extend the latch gates has a circular recess on the wall side from which extends the latch gate which contains the enlarged portion of the stepped alignment sleeve. Within the recess is mounted or positioned a spring member such as a Belleville spring or, alternatively, a coil spring, or an elastomeric spring such as an O-ring, which is adapted to bear against the shoulder formed in the stepped alignment sleeve at the junction of the two differing diameters thereof. Where, for example, the large diameter portion of the sleeve is to receive the large ferrule of an SC connector, whose spring exerts approximately two and two-tenths (2.2.) pounds of force, and the small diameter portion of the sleeve receives the ferrule of an LC type connector, whose spring exerts approximately one and two-tenths (1.2) pounds of force, the adapter spring in the recess exerts approximately one pound of force against the enlarged portion of the alignment sleeve. This one pound force works against the two and two-tenths pounds of the SC connector spring so that it is, in effect, reduced to the one and two-tenths pounds of force of the LC connector spring and the alignment sleeve floats within the chamber formed by the latch gates, thereby preventing degradation of alignment.
The invention is applicable to any of a number of combinations of connectors having dissimilar spring biasing forces with the principles and features thereof being applicable thereto, including the situation, where one of the connectors has no biasing force. A further understanding of these principles and features may be had from the following detailed description, read in conjunction with the accompanying drawings.